/Engine/Plugins/Media/MediaIOFramework/Source/MediaIOCore/Public/MediaCapture.h
make sure the size of the SceneViewport doesn't change during capture.
Return true if the capture was successfully updated. If false is returned, the capture was stopped.
bool UpdateSceneViewport ( [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FSceneViewport](API\Runtime\Engine\Slate\FSceneViewport) > & SceneViewport )